Electrode for glow-discharge device



March 24, 1959 B. SCHWARTZ ELECTRODE FOR GLOW-DISCHARGE DEVICE FiledMarch 16. 1954 INVENTOR BERNARD SCHWARTZ ATTORNEY 2,879,433 ELECTRODEFOR GLOW-DISCHARGE DEVICE Bernard Schwartz, Watertown, Mass., assignorto Sylvania Electric Products Inc., a corporation of Massachusetts Thepresent invention relates to gaseous discharge devices.- In particular,the invention is concerned with gaseous discharge tubes for controllingguided transmission of radiant energy, and specifically to keep-aliveelectrodes and methods of making keep-alive electrodes for such tubes.

In microwave transmission-control tubes Where the invention findsparticular value, it is .customary to employ a keep-alive electrode inassembled relation with. gapforming electrodes for maintaininga: limitedvolume of gas in the gap region in weakly ionized condition. Intransmit-receive tubes, for example, this ionization renders the'jtubeinstantaneously responsive to. highlevels of input radiant energy tobreak down in an arc discharge... In such tubes, the keep-aliveelectrode must be of a construction such that it will not causedeteriorationof'the United States i gaseous fill of the tube and will becapable of withstanding the usual severe operating conditions. A seriousdrawback for long tube life is sputtering gf the keep alive materialwhich tends to" change the tube characteristics, and the growth ofwhiskers" at the keep-alive, tending to short-circuit the tube at thatpart. 7

It is an object of the present invention to provide an improvedglow-discharge electrode which may be incorporated in gaseous dischargedevices, prominently as a keep-alive in gaseous transmission controltubes. t I

It is a-further object of the present inventionto provide agaseous'transmission control tube embodyinga keep-alive electrodeexhibiting properties promoting long tube life.

A still further object of the invention is the provision of an integralkeep-alive electrode of a form readily made and incorporated intogaseous discharge devices.

Partially reduced or semiconducting titania has been found to exhibitdesirable keep-alive characteristics, prominently promoting longtransmit-received tube life. However, there are practical diflicultiesinvolved in incorporating bodies of material in keep-alive electrodes.There exists a need for a keep-alive exhibiting optimum properties forsuccessful operation of such tubes with physical characteristicspromoting manufacture by simplified and direct techniques.

In an illustrative embodiment, demonstrating features of the presentinvention, a keep-alive electrode of zirconium metal is incorporated ina gaseous transmission-control tube. The keep-alive electrode ofzirconium is headed with a vitreous insulating sheath, and is treated ina restricted region to obtain desired keep-alive properties. Thiskeep-alive subassembly is incorporated into the control tube by suitabletechniques, as described in copending application Serial No. 237,258,filed by Paul Gates, now Patent No. 2,740,186, issued April 3, 1956.

In accordance with further aspects of the invention, the keep-aliveelectrode has an active region provided with a layer or surface of thesemiconductive, refractory oxide of the keep-alive metal.Advantageously, this active layer or region is formed in situ byoxidation. One method found suitable for processing the keep-aliveinvolves beading or sheathing the keep-alive metal to provide awell-defined surface serving as the active keep. alive region, andproviding this surface with an oxygendeficient oxide layer byelectrolytic or anodic oxidation. A. further effective method for situtreatment includes the steps of developing the oxide at the activeregion by heating in air or other oxidizing atmosphere, followed byheating in a controlled reducing atmosphere such as hydrogen to renderthe oxide oxygen-deficient. I

The zirconium thus described combines both properties of being. readilysealed to glass, having an appropriate thermal coefficient of expansion,and being adaptable to formation of a bonded refractory semi-conductiveoxide. Other metals of the zirconium group as titanium and hafnium maybe used in broadly applying an aspect of this invention or by joiningsuch metal to a glass-sealing lead and forming an oxide in situ on suchmetal.

The above and still further objects, features, and advantages of theinvention will be best appreciated by reference to the followingdetailed description when taken in conjunction with the drawings,wherein:

Fig. 1 is an enlarged elevation, with parts sectioned for clarity, of aportion of an illustrative keep-alive asly;

Fig. 2 is a greatly enlarged detail of the keep-alive of Fig. 1; andFig. 3 is an elevation with parts sectioned, of an illustrative gaseoustransmission control tube embodying features of the present invention.

Reference will now be made to the subassembly and processing of akeep-alive electrode, illustrative of, the present invention,preliminary to final mounting and orienting in relation to thegap-forming electrodes of the well-known gaseous transmission controltubes. As seen in Fig. 1, the keep-alive electrode 10 includes aconducice tive zirconium body 12, and is provided with an insulatingsheath or bead 14 as of glass covering the body 12 except for a limited,well-defined region 12a. With zirconium as the keep-alive material,advantages are realized in re spect to simplicity since the zirconiummay directly serve as a terminal and may have a directly bondedglas'ssheath 14.

The electrode body 12, is initially enclosed in the insulating sheath 14except for the active face region 12a, which is to be exposed in thebreakdown or discharge gap of the tube, by inserting the electrode body12 in a glass tube and subjecting the assembly to appropriate sealingtemperatures to bond the sheath to the zirconium body. For example, ahard glass tube of the Kovarsealing glasses, such as Corning #7052, issuitable for sealing to the zirconium. A heavy glass button 16 is addedfor ultimate sealing in place, as will be clear later. In anadvantageous illustrative process the sheathed keep-alive zirconiumelectrode 10 has its active exposed face rendered semiconductive andrefractory in situ.

One method of treatment involves anodic or electrolytic oxidation byimmersing the active face region 12a of the keep-alive electrode 10 in asuitable electrolyte, such as nitric acid, and applying apositivepotential to the keep-alive electrode serving as an anode. This may beaccomplished by directly connecting the positive potential with anappropriate cathode, as a platinum cup receiving the electrolyte.Details of an anodic oxidation treatment may be found in an article inthe Journal of the Electro Chemical Society, vol. 100, #12, pages 531-537 of 1953. The anodic oxidation treatment transforms the exposedregion of the zirconium electrode into an adherent, semiconductive andrefractory zirconium oxygen-deficient oxide layer having highlydesirable keepalive properties.

A further method of treatment in situ of the keep-alive electrode toimpart desired semiconductive properties to its exposed region is byheating the exposed area in air to form zirconium dioxide. Thereafter,the metallic oxide area is reheated in a reducing atmosphere, such ashydrogen, and at temperatures ranging from approximately 500 C. to 1100"C., and for an appropriate period gauged to accomplish only partialreduction so as to yield a semiconductive adherent oxide.

The keep-alive electrode as shown in Figs. 1 and 2 is sealed to ametal-to-glass sealing supporting sleeve 18, by arranging the keep-aliveelectrode 10 concentrically of the sleeve 13 and axially displacing theelectrode While developing localized heat at the end of the sleeve 18remote from the head or fiange end 20.

This intermediate assembly is then joined to a conical gap-formingelectrode 22, as shown in Fig. 3, by brazing the lateral flange 24 ofthe electrode to the flanged end or head of the sleeve 18, care beingexercised to obtain proper centering and spacing of the exposed andtreated face 12a of the keep-alive relative to the tip of thegap-forming electrode 22. conventionally, the active face 12a of thekeep-alive electrode is spaced a few thousandths of an inch from theopening in the tip of the discharge or gap electrode 22, both radiallyand endwise. Assembly of the gap-forming electrode 22, with a furtherconical gap-forming electrode 26, as in the illustrativetransmit-receive tube of Fig. 3, will best be appreciated by referenceto the mentioned applications. The foregoing assembly method is morefully detailed in the above mentioned application Serial No. 237,258,now Patent No. 2,740,186.

Briefly, the gap-forming electrodes 22, 26, are arranged across a lengthof wave guide 30 having flanges 32, 32' for connection to a microwavesystem. The ends of the wave guide 30 have resonant windows 34, 34'.Electrode 26 may be of deformable construction for critical adjustmentby engagement from the exterior of the waveguide 30, as by provision ofa complementary body (not shown) within the electrode 26. With multipleelectrode pairs, the gaps are normally spaced along the waveguide adistance equal to an effective quarter wavelength at the centerfrequency of the transmit-receive device.

The waveguide 30 is conventionally filled with an electron capture gas,preferably a noble gas such as argon, mixed with a quenching gas, suchas water at a total pressure of the order of twenty-five millimeters ofmercury.

In operating the illustrative transmit-receive tube of Fig. 3, a currentis passed between the keep-alive electrode 10 and the dischargeelectrode 22; normally several hundred volts is applied between thekeep-alive electrode 10, directly serving as a terminal, and thegap-electrodes 22, 26, establishing a glow discharge. The keep-alivepotential maintains a limited volume of gas ionized in a confined regionadjacent the gap. Upon incidence of high level signal bursts, thelimited volume of weakly ionized gas promotes an abrupt formation of anintensely ionized discharge thereby switching the waveguide transmissionpath from one in which low level signals are transmitted, to one inwhich high level signals are almost entirely reflected. The use of suchdevices is well known, and requires no further elaboration.

From the foregoing, it can be appreciated that keepalive electrodesembodying features of the present invention exhibit desirable keep-aliveproperties and are mechanically suited to be incorporated in a varietyof tube constructions without extreme fabrication difiiculties,especially in view of the physical geometry of environment electrodeconstructions, and the frequently critical spacing requirements.

From the foregoing disclosure of the several aspects of the presentinvention, those skilled in the art will find varied applications of theinvention as well as various further modifications. Accordingly, theappended claim should be interpreted broadly, consistent with the spiritand scope of the invention.

What is claimed is:

A keep-alive electrode for a glow-discharge device comprising anelongated zirconium rod having a terminal end and a discharge end, alayer of semi-conductive zirconium oxide adhering to the lateral endsurface of the discharge end of said rod, and a glass sheath bonded toand completely covering the discharge end of said rod except for saidlateral end surface.

References Cited in the file of this patent UNITED STATES PATENTS2,006,081 Anderson June 25, 1935 2,241,362 Gustin May 6, 1941 2,249,672Spanner July 15, 1941 2,453,118 Buckingham Nov. 9, 1948 2,460,738Francis Feb. 1, 1949 2,560,347 Peck July 10, 1951

